Alternating-current electromagnet with armature



March 27, 1951 L. J. GOLDBERG ALTERNATING Inven tor; Le om J Gold beT b@w m y H is Attorney.

Patented Mar. 27, 1951 UNITED STATES PATENT OFFICEALTERNA'I-flNG-CURRENT ELEQIRO- MAGNET WITH ARMATURE Leon J. Goldberg,Schenectady, N. Y., assignor to General Electric Company, a corporationof New York Application July 26, 1949', Serial No. 106,917

1- Claim. 1

This invention relates to alternating current electromagnets, and moreparticularly to alternating current electrcmagnetsof the shaded poletype. The principal object of the invention is to provide an improvedtype of construction for such electromagnets.

Shading coils commonly are used in the pole faces of alternating currentelectromagnets to provide a shift in time phase of a portion of themagnetic flux in order to' produce a continuous pull for attracting andholding an armature. In order to provide such a shading coil, themagnetic path is split and one part of the magnetic path. is surroundedwith a conducting loop. The presence of such a loop, because of thecurrent which is induced in it, produces an additional component ofmagnetic flux in the core of the electromagnet which results in a timedelay in the main flux in the portion of the magnetic circuit which theshading coil encircles, thuscaus= c ing the magnetic flux in thisportion to pass through zero at a later point in the cycle than the fluxin the other portion. When the pull due to the magnetic flux outside theloop is zero; there is a finite pull by the flux within the loop, andwhen thepulldue to the-magnetic flux within the loop is zero, there is afinite pull by the flux outside the loop; thus, a continuous magneticpull is provided whereby chattering or vibration of the armature isminimized.

The magnetic cores of alternating current electromagnets are usuallylaminated to prevent ex' cessive eddy currents in the cores.I-Ier'etofore, in the construction of a magnetic core having a shadingcoil in a pole face thereon, it has been customary to provide a recessin the pole face perpendicular to the plane of the laminations. In this.recess. is located a portion of the conductive loop which. encircles apart of the magnetic path to form the shading coil. This construction isentirely satisfactory for holding an armature or other member once ithas been attracted to the core; however, it has been found that suchconstruction may cause the armature to stick, or not to retractimmediately when ex citation is removed from the electromagnet,particularly if there is good magnetic contact between the core and thearmature, this eifect being due to the remanent or residual flux causedby the shading coil within the coil and completing its loop around theembedded portion of the conductor which forms the loop.

It is an object of my invention to reducev the remanence caused by theshading. coil and thereby to prevent the. armature from sticking becauseof this remanence.

Inv carrying out my invention in one form, I provide an electromagnethaving a U-sha'ped laminated core. An armature, which bridges the endsi? the core in the closed position, is operexcitation coil l3;

2. ated by the magnetic attraction of the electromagnet. The end surfaceon each leg ofthe core has a recess across it parallel tothe plane orthe Iam-inations. A single loop shading coil, which encircles a portionof the magnetic path inthat leg of the core, is positioned in each suchrecess. In order to minimize the residual magnetic flux encircling thepart of the shading coil embedded in the recess, during the timeimmediately following the tie-energizing of the electromagnet; aseparator of non-magnetic material is provided between two of thelaminations abutting on each such recess. This introduces into the pathof the magnetic flux component aroundthe coriduster forming the shadingcoil, reluctance of sufficient magnitude to reduce the remanent value ofthis-flux sufficiently to prevent the armature from stickingdue tosuchremanent but not sumcient to prevent flux around the shading coilduring energizationof the electfo' magnet from reducing the chatter ofthe arma ture.

For a clearer and more complete-understanding of my invention, referenceshould be had to the accompanying drawing, Fig. I of which is aside viewin elevation of one embodiment of the inven tion; Fig. 2 is a sectionalview along theline 2"'-2 of Fig. 1; Fig. 3- is a partial end- View ofthe core of the device shown in Fig. 1 along the line 3*, with theexcitation coil and shading coil removed; while Fig. 4'- isaperspec'tive- View of the core if Fig. l with the excitation coilremoved but with theshading coils in position.

Referring to Fig. 1- of the drawing, atypical device embodying myinvention is designated generall'y'by the numeral Ill. The device lfl'has' a U-shaped stationary core, or frame portion H and a movablearmature I21 On one leg of core i l is positioned amulti-t'urnalternating current Together, core' I I and excite tion coil3 comprise an electromagne't which at: tracts" armature I-Z when coi'l'I"? is energized, and thereafter holds the armature in' the closedposi-' tion illustrated in Fig. as long as the electro-* magnet remainsenergized; Armature I2 isbiased by springs M or other suitable meanswhich-- pull= armature 2 away from core I i when" the electro' magnet isde-energized. The pullof theelect ro magnet is strong enough to overcomethe pull of springs M whencoil l 3 is enei'g-izedz' Armature l2, as bestseen in Fig. 2, is composed of a plurality of fiat laminations l5 of magnetic material, preferably steel, separatedby lay as It; of electricalinsulating material in order to minimize eddy currents the armatureduets alternating magnetic flux. Gore H is composed principally ofsimilar flat lam-i-nations H oi mag: netic material separated bylayersI-B oi elee't'ri cal insulating material In" the: bi'ght; portion o'fcore H is a separator, or spacer I9 of non-mag netic material. Spacer i9is perpendicular to the plane of laminations I! and covers the entirecross sectional area of core II, completely separating the core into twolaminated portions. Each upper horizontal surface of the legs of core IIis provided with a slot or recess 20, one of which is clearly shown inFig. 3. Each recess 20 extends entirely across the end surface, or poleface of the core leg in which it is located parallel to the laminationsIT. The legs of frame I I may be termed polar projections inasmuch asthese legs contain the magnetic poles of the electromagnet formedjointly by frame II and exciting coil 13; likewise, the end surfaces ofthe legs of frame I i may be called pole faces.

Each leg of core H is provided with a nonmagnetic separator 2! ofsuitable thickness which abuts on recess 20, thus providing a magneticseparation between the portions of each leg of the core which lie onopposite sides of the separator 2|. Positioned in recesses 20, as seenbest in Fig. 4, are shading coils 22 which are composed of a singleclosed loop of electrically conductive material such as copper. Eachcoil 22 encircles a portion of the core leg adjacent the end, or poleface against which armature l2 abuts, thus providing an additionalcomponent of magnetic flux due to the current induced in the shadingcoil, which has the effect of retarding the portion of the main fluxencircled by coil 22, thereby reducing the tendency of the armature tochatter.

, When coil I3 is energized, the restraining force of springs 14 isovercome and armature i2 is attracted and held in engagement with coreii, inthe position illustrated in Fig. 1. This forms a magnetic circuitaround the loop formed by members I l and l 2 in which oscillatingmagnetic flux is present, the oscillations being at the frequency of thealternating current in coil l3. When coil I3 is deenergized, the flux inthe loop formed by core II and armature l2 decays gradually inaccordance with the hysteresis characteristic of the loop. If spacer l9were not present in the bight portion of frame H, the hysteresischaracteristic might, under some circumstances permit an amount ofresidual flux sufilcientto cause the armature l2 to stick closed againstthe pull of springs l4 even after the removal of coil excitation. Spacer59 increases the reluctance of the loop formed by members H and I2sufiiciently that the magnetic flux in this loop always decays to a lowenough value when coil I3 is de-energized that the pull exerted thisresidual flux is insuificient to cause sticking of the armature.

Shading coils 22 also tend to cause armature l2 to stick when coil I3 isde-energized. The principal function of coils 22 is to produce acomponent of flux in a separate path in order to change the time phaseof a portion of the main magnetic flux and thereby to prevent chatter orvibration of the armature. The effect of this addition flux componentmay be to cause sticking of the armature under some conditions, theseconditions depending on where on the voltage wave the circuit is opened.In order substantially to counteract this effect, I provide nonmagneticlaminations or separators 2! which create relatively high reluctancepaths for the components of magnetic flux surrounding the portions ofcoils 22 which are embedded in recesses 20. This is illustrated by thearrow 23, which is shown in Fig. 2 encircling the embedded portion ofone coil 22, it being understood that the direction of the flux isreversed during half 4 of each cycle. Nonmagnetic separator 21 issubstantially perpendicular to the path of the flux below coil 22, sothat the reluctance of this path is increased. This causes the componentof flux around coil 2'2 to decay to a lower value when the electromagnetis de-energized, thereby preventing sticking or delayed opening of thearmature due to such flux.

The essential feature of my invention is the introduction of additionalreluctance in the circuit of the component of magnetic flux resultingfrom the shading coil, in order to prevent the sticking of the armaturebecause of the residual flux in this circuit. It will be understood,however, that the use of a nonmagnetic separator 2| is not the onlymanner in which sufficientreluctance may be introduced into thiscircuit. For example, the presence of layers It and I8 of insulatingmaterial between laminations l5 and I1, respectively, may providesufficient reluctance, thus making separator 2| unnecessary. It will benoted from arrow 23 in Fig. 2 that the path of this component ofmagnetic flux is substantially normal to the layers It and 18 above andbelow conductor 22; therefore, one or more layers l6 and one or morelayers is are always present in this path, even in the shortest possiblepath for this component of flux, providing recess 20 in wider than thethickness of laminations l5 and H. Consequently, if layers It and I8 areprovided with sufficient reluctance, they alone may supply thereluctance that is required.

It will be noted in Figs. 1 and 4 that shading coils 22 in this typicalapparatus embodying my invention are disposed on the two legs of core llso that they are symmetrical with respect to a pull axis extendingvertically through the geometrical center of the upper surface ofarmature l2. The eifect of this is to prevent unbalance of the forcenecessary to pull armature l2 away from core II when coil I3 isde-energized. The unbalancing effects of the two shading coilscounteract each other, both laterally and longitudinally, when theelectromagnet is constructed in the manner illustrated, causing the pullaxis to remain substantially centralized with respect to the uppersurface of armature l2.

While I have illustrated and described one preferred embodiment of myinvention, together with one modification thereof, additionalmodifications will occur to those skilled in the art. Therefore, itshould be understood that I intend to cover, by the appended claim, allsuch modifications as fall within the true spirit and scope of myinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

An electromagnet device comprising a U -shaped frame of laminatedmagnetic material in which the laminations lie parallel to a planecoinciding with the center lines of the legs of said U, a firstnonmagnetic separator in one leg of said U parallel to said laminationsseparating said leg into two laminated portions, said first separatorbeing a predetermined distance from one side of said U-shaped frame, asecond nonmagnetic separator in the other leg of said U parallel to saidlaminations separating said other leg into two laminated portions, saidsecond separator being an equal distance from the other side of saidframe, a first recess in the end surface of said one leg parallel tosaid laminations, said first separator abutting the bottom of said firstrecess, a first shading coil positioned in said first recess surroundingthe portion of said one leg lying between said recess and said firstside, a second recess in the end surface of said other leg parallel tosaid laminations, said second separator abutting the bottom of saidsecond recess, a second shading coil positioned in said second recess 5surrounding the portion of said other leg between said second recess andsaid second side, an exciting coil positioned on said frame, asymmetrical U-shaped laminated armature operatively positioned adjacentthe end surfaces of 10 said legs, the end surfaces of the legs of saidarmature arranged to abut respectively said end surfaces of the legs ofsaid frame when said exciting coil is energized, and means biasing saidarmature away from said frame.

LEON J. GOLDBERG.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

